You can identify a scheduled activity as it has extra details on the right hand side - specifically the start and end date. It will also have a Meeting Reports section to keep track of the time reported by each attendee.
When you action the activity, you will have to report on it. This is the same as using the "Create Report" link:
You can only report once. As you create the Activity, it will prompt you to fill in the schedule time for the meeting. You cannot have billable time and a scheduled meeting as the meeting will be where you log your time.
As other attendees log their time and notes, the meeting Time Spent will not tally, or update, as their time is kept within their report activity. When you need to bill for this time, you will see each report activity nested within the meeting activity, and the time reported by each user.
To find a meeting report, you need to find the parent activity. Meeting reports are hidden from the activities associated tabs, but the meeting activity itself will be visible and searchable.